Density
Objective: To examine the density of water and how it varies
with temperature and the amount of materials dissolved in
it. Relative density is also examined.
The weight density of a material is the weight of a given
volume unit of the material divided by that volume unit. An
example is that a 1 cubic foot volume of water weighs 62.4
pounds. The density of water is then 62.4 pounds per cubic
foot.
The density of water varies with temperature. The maximum
density occurs slightly above freezing. The density of water
then goes down for temperatures greater than or lower than
4 degrees C. This is good for us in that lakes do not freeze
solid in the winter killing all life in them.
The density of water also varies with the amount of material
that is dissolved in it. As more material is dissolved in
1 gallon of water then that gallon will weigh more (the total
weight is equal to the weight of the water plus the weight
of the material dissolved in it). The density is the weight
of the gallon divided by 1 gallon. Since the weight of the
gallon of water with material dissolved in it weighs more
that pure water then the density of the solution also increases
from that of pure water.
The density of water is often taken as a standard and the
density of other materials compared relative to it. The relative
density of water is the density of water over the density
of water, 62.4 pounds per cubic foot over 62.4 pounds per
cubic foot, so that it is 1.0. The relative density of a rock
that is 2 times as dense as water is the density of the rock
(124.8 pounds per cubic foot) divided by the density of water
(62.4 pounds per cubic foot) to give 2.0. The relative density
of steel is 7.7 and that of mercury is 13.6.
Icebergs
Icebergs are comprised of water that has frozen, similar
to ice cubes in a drink. The density of the ice is slightly
less than water, causing them to float. Roughly 9/10 of the
iceberg is below water.
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